Unselecting CONFIG_PRINTK_TIME does indeed prevent the kernel to provide the timestamp but will obviously not prevent your logging system (sys/meta/whatever-log) to add its own one.
(Far less accurate than kernel's one of course).
Which makes dmesg --notime, the only practical answer to your original question (How to remove [%lu.%lu] in dmesg???)_________________

config PRINTK_TIME
bool "Show timing information on printks"
depends on PRINTK
help
Selecting this option causes time stamps of the printk()
messages to be added to the output of the syslog() system
call and at the console.

The timestamp is always recorded internally, and exported
to /dev/kmsg. This flag just specifies if the timestamp should
be included, not that the timestamp is recorded.

The behavior is also controlled by the kernel command line
parameter printk.time=1. See Documentation/kernel-parameters.txt

...
* The 'struct log' buffer header must never be directly exported to
* userspace, it is a kernel-private implementation detail that might
* need to be changed in the future, when the requirements change.
*
* /dev/kmsg exports the structured data in the following line format:
* "level,sequnum,timestamp;<message text>\n"
*
* The optional key/value pairs are attached as continuation lines starting
* with a space character and terminated by a newline. All possible
* non-prinatable characters are escaped in the "\xff" notation.
*
* Users of the export format should ignore possible additional values
* separated by ',', and find the message after the ';' character.

so dmesg is only filtering what between "[" and ']'. Who is adding the timestamp ? You have said the logger, is it possible to hack it ?

The rfc5424 does not exactly appear to me as belonging to the april's joke category of rfcs.
So... feel free... to be on your own.

Well, why should i add rules on bashrc ? why should i process the output of /dev/kmsg in order to filter the damn verbosity ? I want simpler stuff, i want a kernel that puts out clean things, also older kernel (e.g. 2.6.39) are not so verbose.